1. Field of the Invention
The present invention relates to an output control apparatus for hybrid vehicles, and particularly relates to an output control apparatus for hybrid vehicles provided with an idle stop function.
2. Background Art
Conventional hybrid vehicles provided with a motor in addition to an engine as a driving source for travelling are known.
A parallel hybrid vehicle is a type of hybrid vehicle which uses a motor as an auxiliary driving source for assisting the output of the engine. Such hybrid vehicles are designed so as to be able to satisfy the driver""s demands while preserving a remaining state of the charge of the battery, that is, the state of charge of the battery by executing a variety of controls, such as using a motor for supplementing the driving force at the time of acceleration, and charging the battery by deceleration regeneration at the time of deceleration. Such conventional hybrid vehicles are disclosed in, for example, Japanese Unexamined Patent Application, First Publication No. Hei 7-123509.
In order to improve the fuel efficiency, a type of hybrid vehicles is provided with a function for cutting the fuel supply (hereinafter, called a xe2x80x9cfuel cutxe2x80x9d) at the time of deceleration. The fuel cut makes it possible to save otherwise wasted fuel and to improve the fuel consumption rate. Vehicles provided with the fuel cut function are constituted such that the engine speed is lowered while the fuel cut continues, and when the engine speed reaches a predetermined speed (approximately a little higher than that at the time of idling but without stalling), the fuel supply is automatically restarted suspending the fuel cut.
Recently, however, in order to further improve the fuel consumption rate, an idle stop mode is provided, in which the fuel cut continues until the engine stops without restarting the fuel supply even if the engine speed reaches a fuel supply restarting speed, when the driving conditions satisfy certain conditions, that is, when the driver executes a particular operation subsequently to stop the vehicle.
In a hybrid vehicle provided with such an idle stop mode, no problem arises when the driver stops the vehicle as scheduled. However, a problem arises when the driver again accelerates the vehicle in the idle stop mode, because of a change of the driving conditions (such as the conditions of the road or traffic signals), the engine may not be unable to recover the speed and the vehicle may stall, since the engine speed is already below the automatically recoverable speed.
Therefore, when the vehicle is in the idle stop mode, it is necessary to prevent the driver from being subjected to an uneasy feeling due to sudden stopping of the engine or due to a shock caused by the motor entering into the acceleration mode from the deceleration regeneration mode, against the driver""s wishes due to the driver""s operation of the accelerator pedal.
It is therefore an object of the present invention to provide an output control apparatus of a hybrid vehicle, capable of preventing stopping of the engine at the time of returning from the fuel cut mode, and improving the acceleration performance.
The first aspect of the present invention provides an output control apparatus for a hybrid vehicle comprising: an engine (for example, the engine E in the present embodiment), a motor (for example, the motor M in the present embodiment) for assisting the output power of said engine, and a battery device (for example, the battery 3 in the present embodiment) for supplying electric power to said motor; wherein the output control apparatus comprises: an output assistance judgement device (for example, the motor ECU 1 in the present embodiment) for judging whether said motor should assist an output of the engine depending upon driving conditions of said vehicle; a controlling amount setting device (for example, the motor ECU 1 in the present embodiment) for setting the controlling amount of said motor depending upon a driving state of said engine when the output of the engine is judged by said output assisting judgement device to receive assistance; an output assistance control device (for example, the motor ECU 1 in the present embodiment) for carrying out the output assistance of said engine by said motor based on the controlling amount set by said controlling amount setting device; and an engine speed (for example, the engine speed NE in the present embodiment) detecting device (for example, the engine speed sensor S2 in the present embodiment) for detecting the engine speed; a deceleration fuel cut judging device (for example, the idle stop execution judgement flag F_FCEX in the present embodiment) for judging whether the fuel supply is to be cut at the time of decelerating the vehicle; and a deceleration fuel cut returning time permission judgement device (for example, step S026 in the present embodiment), provided with said output assistance judgement device, for permitting engine output assistance by said motor, when said deceleration fuel cut judgement device judges that the fuel supply is to be started returning from the fuel supply cut, and when it is detected by said engine speed detecting device that the engine speed at the time of starting the fuel supply returning from the fuel supply cut is lower than the predetermined engine speed (for example, the emergency motor start permission lower limit engine speed #NEMGMOT in the present embodiment).
The output control apparatus with the above described structure makes it possible to assist the engine with the motor when the deceleration fuel cut return time permission judgement device determines to return from the deceleration fuel cut mode and when the engine speed at that time is lower than the predetermined engine speed. That is, when the driver depresses the accelerator pedal to accelerate the car while the car is in the deceleration fuel cut mode, if the engine speed at that time is below the predetermined engine speed, and when the deceleration fuel cut returning time permission judgement device determines to return from the deceleration fuel cut and when the output power assistance judgement device determines to assist the engine output power by the motor, the engine power for driving the vehicle is supplemented by the motor.
According to the second aspect of the present invention, in an output control apparatus of a hybrid vehicle according to the first aspect, the output control apparatus of a hybrid vehicle comprises a gradual fuel addition device for executing a gradually addition of the fuel supply at the time of returning from the time of the fuel supply cut.
The above described structure allows for the vehicle to be accelerated gradually by the gradual addition of the fuel supply.